1. Field of the Invention
The present relates to image reading apparatus which read optical image data and output them as an electrical signal, and more particularly to image reading apparatus which are intended to have a simplified and miniaturized structure.
The image reading apparatus according to the present invention is applied to input units of facsimiles or reproduction apparatus, for example.
2. Description of the Prior Art
Generally, an image reading apparatus includes a plurality of photosensors arranged in an array and receiving reflected light and/or transmitted light from an original document. The photosensors are scanned to read data of an image in the document as an electrical signal.
As typical photosensor drive systems, there are a matrix drive system and a direct drive system.
FIG. 1 is a perspective view of a sensor substrate of a conventional image reading apparatus employing a matrix drive system.
In FIG. 1, photosensor array 2 which includes a plurality of photosensors disposed on a substrate 1. Array 2 is divided into a plurality of blocks each including a fixed number of photosensors. One-sided terminals of photosensors for each block are connected to a matrix wiring section 3 and the other-sided terminals are connected together to a drive circuit chip 4. Matrix wiring section 3 is connected via a drive circuit chip 5 to a signal processor chip 6.
FIG. 2 is a cross-sectional view of a conventional image reading apparatus using the sensor substrate of FIG. 1.
In FIG. 2, the sensor substrate is fixed to a base 7 and protected by an upper cap 8 covering base 7. Provided on base 7 is a light source 9, the light from which is reflected by an original document 10. The reflected light is focused by a focusing rod lens array 11 onto photosensor array 2.
Drive circuit chip 4 applies a drive voltage sequentially to the respective photosensor blocks of photosensor array 2 to activate the photosensors. Optical data from the activated photosensors are sequentially read as a serial signal by the operation of matrix wiring section 3 and drive circuit chip 5. Such matrix driving causes all the data of photosensor array 2 and hence image data of document 10 included in a scanned line to be read. Thus the whole image in document 10 is read as an electrical signal as document 10 is moved in the direction of arrow A.
As described above, in the matrix drive system, the construction of the drive circuit and signal processor is simplified, so that the number of circuit chips is reduced although many photosensors are disposed.
As shown in FIG. 1, however, when array 2, matrix wiring section 3, drive circuit and signal processor chips 4 to 6, etc., are constructed integrally on substrate 1, matrix wiring section 3 and other wiring sections occupy a relatively large area, which is an obstacle to miniaturization of the whole apparatus.
On the other hand, the direct photosensor drive system includes drive circuit chips corresponding to the photosensors to read optical data as a serial signal, so that the wiring sections do not occupy a large area as is the case with the matrix drive system. Since, however, the direct photosensor drive system mounts many circuit chips, it occupies a large mounting area, thereby rendering it difficult to attain miniaturization. In addition, since the apparatus includes the same number of circuit chips as of photosensors, an increase in cost cannot be avoided. More particularly, in a high-accuracy reader with many photosensors, such a drawback is obvious.
As described above, it is difficult to miniaturize the conventional image reading apparatus.